1. Field of the Invention
The present invention relates generally to a tray for electronic parts. More specifically, the invention relates to a tray used for carrying and inspecting electronic parts, such as semiconductor devices, each of which has ball terminals on its package bottom.
2. Related Background Art
FIG. 1 is a perspective view showing the appearance of a conventional tray for electronic parts.
FIG. 1 shows first and second conventional trays 7A and 7B for electronic parts. The two conventional trays for electronic parts are shown in order to explain conventional problems which will be described later. Since the first and second conventional trays 7A and 7B for electronic parts have the same structure, the structure of the first conventional tray 7A for electronic parts will be described below.
The conventional tray 7A for electronic parts comprises: a substantially rectangular table-like flat portion 7Aa constituting a principal portion of the tray; a plurality of pockets 7Ab, each of which comprises a recessed portion formed in the table-like flat portion 7Aa so as to be adapted to the size of a corresponding one of electronic parts to be housed therein and which are arranged in the form of a matrix; a step-like peripheral edge portion 7Ac which is formed on the peripheral edge portion of the table-like flat portion 7Aa so as to allow a plurality of trays to be sequentially engaged with each other to be stacked up; a side-wall-like edge portion 7Ad which is formed on the bottom side of the step-like peripheral edge portion 7Ac so as to support thereon the table-like flat portion 7Aa and the step-like peripheral edge portion 7Ac; cut-out portions 7Af which are formed by cutting out part of the side-wall-like edge portion 7Ad so as to engage the carrying pawls of a carrying mechanism for carrying the tray; and a cut-out corner portion 7Ae which is formed by cutting out one of four corner portions of each of the table-like flat portion 7Aa and step-like peripheral edge portion 7Ac in order to align the respective trays when the plurality of trays are sequentially engaged with each other to be stacked up.
This conventional tray 7A for electronic parts is used for housing electronic parts, such as semiconductor devices, each of which has ball terminals on its package bottom, to carry and inspect the electronic parts. In order to avoid damage to the ball terminals on the bottom of the package of electronic parts, a through hole for exposing the ball terminals to the reverse surface side of the tray is formed in the central portion of the bottom of each of the pockets 7Ab so that the peripheral edge portion of the bottom of the package of electronic parts is supported on the peripheral edge portion of the bottom of each of the pockets 7Ab. The conventional tray 7A for electronic parts is produced by injection-molding a plastic material or the like.
FIG. 2 is a perspective view showing a state that a plurality of conventional trays for electronic parts are sequentially engaged with each other to be stacked up.
In FIG. 2, the plurality of trays are not particularly distinguished from each other, so that the respective portions of each of the trays are expressed by common reference symbols, such as a table-like flat portion 7a, pockets 7b, a step-like peripheral edge portion 7c, a side-wall-like edge portion 7d, cut-out portions 7f and a cut-out corner portion 7e. 
In order to collectively carry the plurality of conventional trays for electronic parts, the trays are carried in a state that the trays are sequentially engaged with each other to be stacked up as shown in FIG. 2.
In FIG. 1, the first and second conventional trays 7A and 7B for electronic parts are shown in opposite directions to each other in order to explain conventional problems which will be described later. In order to normally stack the plurality of trays, after the directions of the respective trays are coincident with each other so that the cut-out portions 7e of the respective trays are arranged in vertical directions, the respective trays are sequentially engaged with each other to be stacked up as shown in FIG. 2.
The electronic parts 5, each of which has the ball terminals 5a on its package bottom, are housed in the respective pockets so that the ball terminals 5a are directed toward the bottom of the tray.
FIGS. 3A and 3B are perspective views showing states that the conventional tray for electronic parts is carried by a carrying mechanism.
As shown in FIG. 3A, the conventional tray for electronic parts is carried by engaging the carrying pawls 3 of the carrying mechanism with the cut-out portions 7f formed in the sidewall-like edge portion 7d of the tray. Referring to FIG. 3B, conventional problems will be described later.
FIG. 4 is an enlarged perspective view of a part of the appearance of the conventional tray for electronic parts shown in FIG. 1. The construction of the conventional tray for electronic parts has been described above referring to FIG. 1.
In FIG. 4, the respective portions of the tray are expressed by common reference symbols, such as a table-like flat portion 7a, pockets 7b, a step-like peripheral edge portion 7c, a side-wall-like edge portion 7d, cut-out portions 7f and a cut-out corner portion 7e. 
FIG. 5 is a sectional view showing a state that a plurality of conventional trays in which electronic parts are housed therein are sequentially engaged with each other to be stacked up.
As described above referring to FIG. 2, the electronic parts 5, each of which has the ball terminals 5a on its package bottom, are housed in the respective pockets so that the ball terminals 5a are directed toward the bottom of the tray. The respective trays are sequentially engaged with each other to be stacked up so that the side-wall-like edge portion 7d of each tray is mounted on the step-like peripheral edge portion 7c of a tray which is arranged directly below each tray. As shown in FIGS. 5 and 2, the plurality of conventional trays for electronic parts are carried in a state that the plurality of trays are sequentially engaged with each other to be stacked up.
FIG. 6 is a sectional view showing a state that two conventional trays for electronic parts are stacked up so that the table-like flat portions 7a of the trays face each other in order to reverse electronic parts when the electronic parts housed in the conventional tray for electronic parts are inspected from the reverse side.
When the electronic parts housed in the tray are inspected from the reverse side, it is required to reverse the electronic parts. Although some methods for reversing the electronic parts are considered, the electronic parts must be repacked so that the top face of the package of the electronic parts is directed downwards when the electronic parts are reversed while the top face of the tray is directed upwards. However, in this method, it takes a lot of time to repack the electronic parts, and the electronic parts are often damaged by a miss operation.
Therefore, as one method for reversing electronic parts, there is adopted a method for reversing electronic parts, which have been housed in the respective pockets 7b, to move the electronic parts from one tray, in which the electronic parts have been housed, to the other empty tray at a time by reversing the two trays at the same time in a state that the other empty tray is stacked on the one tray so that the top face of the other empty tray faces the top face of the one tray as shown in FIG. 6.
However, in the above described conventional tray for electronic parts, there are various problems as follows.
First, as shown in FIG. 1, the first and second trays 7A and 7B for electronic parts serving to the two conventional trays for electronic parts are provided with the cut-out corner portions 7Ae and 7Be, respectively, in order to align the respective trays.
However, if both trays are directed in opposite directions by mistake to be engaged with each other to be stacked up in a state that the cut-out corner portions 7Ae and 7Be are not arranged in vertical directions, there are problems in that both trays are not correctly engaged with each other due to the existence of the cut-out corner portions 7Ae and 7Be, to damage the side-wall-like edge portions 7Ad and 7Bd of both trays and/or to cause both trays to warp.
As described above, when the electronic parts housed in the tray are inspected from the reverse side, it is required to reverse the electronic parts. Therefore, as shown in FIG. 6, there is adopted a method for reversing electronic parts by reversing two trays in a state that the two trays are stacked up so that their top faces face each other.
However, in this method, the top faces of the two trays face each other, so that the depth of each of the pockets 7b is doubled to be twice or more as large as the height of each of the electronic parts. Therefore, there are some cases where the electronic parts remain being inclined in the pockets 7b when the two trays are reversed to reverse the electronic parts. As a result, there are problems in that the electronic parts are damaged and that it is determined that the electronic parts are not good since inspection can not normally be carried out although they are non-defective parts.
Therefore, in order to avoid the problems in the method for repacking electronic parts to reverse the electronic part and in the method for simultaneously reversing two trays while the top faces of the two trays face each other to be stacked, there is also another method for reversing electronic parts by simultaneously reversing a plurality of trays in a state that the trays are sequentially engaged with each other in the same direction to be stacked as shown in FIGS. 2 and 5. As shown in FIG. 5, in this method, the electronic parts are reversed in a state that the electronic parts are housed in the pockets 7b having a depth corresponding to the depth of each of the electronic parts. Therefore, the electronic parts are not inclined after reversal, and it does not take a lot of time unlike the method for repacking electronic parts.
However, when the electronic parts are inspected from the reverse side after all of the trays are reversed, the trays must be carried one by one while the trays are reversed as shown in FIG. 3B.
When the tray is carried without being reversed as shown in FIG. 3A, the cut-out portions 7f formed in the side-wall-like edge portion 7d can engage the carrying pawls 3 of the carrying mechanism to surely carry the tray. On the other hand, when the tray is carried while being reversed as shown in FIG. 3B, although the carrying pawls 3 engage the step-like peripheral edge portion 7c to carry the tray, there is no portion for engaging the carrying pawls 3 in a direction perpendicular to the carrying pawls 3, so that there is a problem in that there are some cases where the tray drops due to side slip while the tray is carried.